Electric power control by use of electronic devices is becoming increasingly important due to an increase in electric power consumption of CPUs (Central Processing Unit) as a result of performance advancements. Conventionally, electronic devices are equipped with such a function as power-saving mode called “suspension” or “hibernation” in order to reduce electric power consumption while users are not using the electronic devices.
The power-saving mode function works so that, before a user turns off a power supply of an electronic device, the electronic device transfers, to a non-volatile storage device (hard disk), information which is stored in a volatile storage device (memory). Then, the electronic device transfers the information back to the volatile storage device when the user turns the power supply back on. This allows the user to resume his/her operation in a state identical to that immediately before the power supply was turned off. Although this function is widely implemented in various electronic devices, the function is only available while a user is not using an electronic device at all. This is because operations of all of components included in the electronic device become suspended while the above function is taking effect.
Meanwhile, timings, with which a computation load is applied to a CPU, are limited. Therefore, such a method is possible in which, even while a user is using an electronic device, electric power consumption is dynamically reduced by suspending, with predetermined timings, part of components included in the electronic device (it is generally called “degenerate operation” when an electronic device is operating while part of components is suspended). Alternatively, another method is possible in which all the devices are made to operate by intensively supplying electric power only when a computation load is applied, and electric power consumption is therefore efficiently distributed.
For example, Patent Literature 1 discloses an image capturing device that simultaneously achieves an improvement in start-up performance and a reduction in electric power consumption. In a case where an image is to be captured with the use of a camera, the image capturing device enhances image capturing performance by temporarily increasing a clock frequency of a CPU. Patent Literature 2 discloses a device that controls an operating frequency of a CPU in accordance with a process to be executed. In a case where the device receives user input, the device sets a clock frequency of the CPU to a predetermined rate.
Patent Literature 3 discloses an information processing system that includes a processor whose operating speed is changeable. The information processing system is designed to reduce electric power consumption by reducing, within tolerance of a response time, an operating frequency of the processor. Patent Literature 4 discloses an information processing device that eliminates delay time of low priority tasks. The information processing device enhances processing stability by eliminating, from execution time, delay time that has resulted from interrupt processing while electric power is controlled.
Patent Literature 5 discloses a processing system that executes, at a lower electric power consumption rate, a process that involves a time limit for a response. The processing system includes a hardware mechanism that changes, during a system operation, an operating frequency and a power supply voltage which are to be supplied to a processor.